SDP wz 66 Grom (Poland, Tier-8, TD, premium, mechanics: a gun with a deep rifled barrel)
Historical Reference: The anti-tank self-propelled gun SDP wz 66 Grom, from the late 1950s to early 1960s, was designed with consideration of Soviet experience in developing similar vehicles. The armor was intended to withstand hits from existing and future NATO tanks, and a gas turbine engine was planned to enhance mobility.
Several types of guns were considered for armament, including those with deep rifling. However, it was impossible to implement some of the ideas due to the technological limitations of the time. All developments remained on paper. 
